This invention relates to a lubricating system for an engine and more particularly to a separate lubricating system that insures that the desired amount of lubricant will be supplied to the engine under all running conditions and only when the engine is running.
Heretofore it has been the practice to lubricate two cycle internal combustion engines by mixing lubricant with the fuel supplied to the engine. Although such an arrangement has the advantage of simplicity, it results in excess consumption of lubricant because it is necessary to maintain a lubricant/fuel mixture that will supply the most severe condition under which the engine is expected to operate. Hence, excess lubricant is supplied to the engine under most running conditions.
To avoid these problems, it has been proposed to provide a separate lubricating system for two cycle engines. One type of system is disclosed in the co-pending application entitled "Lubricating Oil Supplying System For A Two Cycle Engine", Ser. No. 862,984, filed Apr. 7, 1982 in the name of Yoshinobu Yashiro and assigned to the Assignee hereof. As is disclosed in that application, a reciprocating type of lubricating pump is driven by the engine and supplies a finite amount of lubricant during each cycle of its operation. A delivery valve is interposed in the outlet from the lubricant pump and controls the amount of lubricant supplied to the engine by sequentially supplying lubricant to the engine or returning lubricant back to the inlet side of the pump. The duty cycle of the valve is changed in response to engine running and other condition so as to control the amount of lubricant supplied.
Lubrication systems of the type described are extremely effective in providing good control of the lubricant, adequate lubrication under all circumstances and a minimum of lubricant consumption and smoke in the exhaust of the engine. However, there is always the possibility that lubricant may be carried entrain air. If air is entrained in the lubricant, then the duty cycle of the valve may not provide adequate control of the amount of lubricant supplied. That is, if there is air in the lines the lubricant will expand and contract and displace lubricant so that in a given time period of supply of the flow controlling valve, varying amounts of lubricant may be supplied.
It is, therefore a principal object to this invention to provide an improved lubricating system for an engine that will insure that the desired amount of lubricant is supplied under all conditions.
It is a further object to this invention to provide a lubricating system for an engine wherein the problems of air entrainment in the lubricant are minimized.
If the conduit between the lubricant pump and the flow controlling valve is long then there is an increased possibility of variations in the amount of lubricant supplied due to air entrainment. By keeping the conduit as short as possible, the effect of air in the lubricant may be minimized.
It is, therefore, a still further object to this invention to provide an improved arrangement wherein the distance between the lubricating pump and the delivery valve is minimized.
Since it is readily acknowledged that air can be entrained in the lubricant in the lubricating system, it is also desirable to design the system in such a way that the air will be purged from the system before it can be delivered to the engine.
It is, therefore, a still further object to this invention to provide an improved arrangement which will insure that air entrained in the lubricant can be purged from the system before it is delivered to the engine.
It is a further object to this invention to provide a delivery valve for a lubricating system that is oriented in such a way that the return lubricant will also bleed the air out of the system.
A further problem with separate lubricating systems for engines and particularly two cycle engines is that lubricant may drain into the engine after the engine is shut off. If this occurs, numerous problems can arise. Not only is oil consumption increased, but also the likelihood of smoke in the exhaust is increased. Furthermore, the lubricant flowing into the engine may foul the spark plug and make engine running uneven or, in extreme cases, make starting impossible.
It is, therefore, a still further object to this invention to provide a lubricating system for an engine that will insure that lubricant can not drain into the engine when the engine is shut off.